Advice please regarding hatching eggs.

If they haven't hatched by day 26 then they are highly unlikely to. A couple of days late is one thing but 5 means they have almost certainly died in shell if they were fertile. That they rattle also does not sound good to me although to be fair I have never shaken one to find out I suppose this would happen once the chick had internally pipped into the airsac. If you can't feel any movement and there is no cheeping then it is time to take them away.

What I would do is make a hole in the blunt end to confirm what has happened. In the unlikely event there is signs of life they can be returned otherwise you can examine the chick to see if there is an obvious reason it didn't make it. In my experience there is rarely anything obvious and I therefore don't do it anymore as it is fairly unpleasent.

As to preventing it in the future, I don't have much advice as I usually use an incubator. I have helped out hatchlings but that requires a great deal of intervention and observation which is fine with my incy and it's clear top and I have had excellent results. It is a different matter with a broody and the one time I tried it in that situation it was unsuccessful and I would not attempt it again.